Hai Zhou Yu

Effect of Preformed Angle in Lap Zone on the Failure Procedure of Adhesively Bonded Aluminium Joint

The effect of the preformed deflection angle in the lap zone on the failure mode and the stresses distribution in the single-lap joint made of the epoxy adhesive and the aluminium adherend was investigated using elasto-plastic finite element method (FEM) and the experimental method of the shear strength testing. The failed surfaces were studied with the diagrams of scanning electron microscopy (SEM). The results from the numerical simulation showed that all the peak stresses in adhesively bonded single lap joint were decreased first and increased again as the preformed deflection angle was increased from 00 to 150. The lowest values occurred when the angle was taken as 100 and its strength is 22.1% higher than that of the standard one as the peak stresses were decreased and the stress distributed more evenly. The SEM images also show that the failure mode of the joint was transmitted from the adhesion to the mixed one as the deflection angle increased.

Testing and Analysis of the Inner Stress in Adhesive Coating Layer Using Strain Gauges and Finite Element Method

The residual stress in epoxy adhesive layer deposited on metal and other substrate at room temperature is studied. With embedded strain gauges in arranged depth of epoxy layer, the strain changes in the adhesive layer induced by the curing procedure and the changes of ambient temperature were measured to evaluate the changes of residual stress in place during a period after the curing procedure finished. The actual strain in epoxy adhesive layer from curing is used to estimate the residual stresses in it. While taking the strain obtained from the surface of the adhesive layer as free strain, the residual stress can be calculated and presented a strongly cyclic variation with a period of 24 h. The inner stress is also analyzed using the finite element method.

Discussion on High-Quality Curriculum Construction of Welded Structure in Local Comprehensive Universities

The curriculum construction is a very important work leading to the excellent course. Welded Structure (including 40 class hours) is one of main and compulsory course for the major of Material Molding and Control Engineering in our university. It is very important and necessary to construct the course in time. Based on the project of High Quality Curriculum Construction for Welded Structure undertaken by the authors, this paper makes a discussion on the original ideas, goals and contents, strategies and measures of the project. Meanwhile, the course construction and reform of Welded Structure are introduced from following aspects, such as curriculum setting, teaching contents and methods, teaching staffs, teaching quality management and supervision, online teaching resource construction. The purpose of the paper is to provide beneficial references and experiences to facilitate the further curriculum construction and reform in higher school.

Microstructure and Mechanical Properties of Mo2FeB2 Based Cermets Containing SiC Whisker

Four series of cermets with the SiC whisker content between 0 and 1.0 wt.% were prepared by vacuum sintering. The transverse rupture strength (TRS), hardness (HRA) and fracture toughness (KIC) were also measured. The SiC whiskeraddition was located at the grain boundaries, which prevented grain boundary migration and restrained the grain growth. However, an increasing SiC whisker content decreased the wettability of the binder on the Mo2FeB2 hard phase. The highest TRS and fracture toughness was found for the cermets with 0.5 wt.% SiC whisker addition, whereas the cermets without SiC whisker addition exhibited the maximum hardness.

A Study on Normal Stress Distribution and Failure of Adhesively Bonded Joint under Cleavage Loading

The normal stress distributed in the mid-bondline of the adhesively bonded joint under cleavage loading was investigated using the elastic finite element method (FEM) and the strain gauges method to reveal the real normal stresses distribution in the metal-to-metal joint while the load was increased. The results from the finite element analysis (FEA) showed that there is always a peak stress of the normal stress Sy in the mid-bondline occurred at a point close to the loading pin axis. When the load was increased from 0.5 kN to 3 kN, there was also a point located at about x = 16mm along the length of specimen where there is without any normal stress at all. The result of stress Sy from the FEA is nearly the same as that one obtained from the strain gauges method. It was also found that there was a evidently hardness change in the bonded zone of the adherend made from structural steel or pure copper, which can be used to explain the procedure of the joint and discuss the distribution model of the normal stress Sy in the joint under the cleavage loading.

Research on Effect of Cr3C2 Addition on Microstructure and Mechanical Properties of Ti(C,N)-Based Cermets

Four Ti (C,N)-based cermets with Cr3C2 content of 0.3%, 0.6%, 0.9% and 1.2 % in mass ratio were sintered in vacuum at 1430oC, 1450oC, 1465oC and 1480oC. The mechanical properties of the specimens were determinted and microstructures were observed using the scanning electron microscope (SEM) to study the effect of Cr3C2 content on mechanical properties and microstructure. The results show that the four Ti (C,N)-based cermets sintered at 1465oC have the best overall mechanical properties; and among them, the cermet with 0.6% Cr3C2 has the best overall mechanical properties, i.e. transverse rupture strength (TRS) 1967MPa, hardness 1556HV and fracture toughness (KIC) 9.5MPa.m1/2. With the increase of Cr3C2 content, the black core volume fraction firstly increases and then decreases, the white core decreases in a progressive and continuous manner, the rim phase firstly increases and then decreases, the binder phase firstly decreases and then increases.

Effect of Carbon Content on Microstructure, Mechanical Properties and Wear Resistance of Ti(C,N)-Based Cermets

Ti(C,N)-based cermets with three carbon contents are prepared by sintering in vacuum. The effects of carbon content on the microstructure, mechanical properties and wear resistance of Ti(C,N)-based cermets were investigated. The results show that the grains refine gradually and the hard phase core becomes smaller when the carbon contents increases. The mechanical properties closely relates to the carbon content. With the increase of carbon content, the furrows created by grains cutting are getting narrower and more intensive. When the carbon content reaches 0.8%, a large quantity of wear debris bonding blocks are attached on the wearing surface. In this condition, the Ti(C,N)-based cermets are of the minimum wear weight loss and the best comprehensive mechanical property.

Testing and Stress Analysis of Curing Process of Epoxy Adhesive Coating

Three groups of strain gauges were embedded in the epoxy adhesive coating deposited on the steel substrate with different depths. The transverse and longitudinal strains during the curing process were tested. It was found that the transverse and longitudinal strains decreased remarkably when the curing time was lower 24h. At a longer curing time, the strains almost kept steady. In addition, the more close to the surface of epoxy adhesive coating, the higher the strains were. The solidification contraction stress in the epoxy adhesive coating during the curing process were also estimated, and the attempts were made to relate them to the restrained contraction of the epoxy adhesive coating.

Colloidal Dispersion of High Solid Loading ZnO Powders with 2 wt% Al2O3 Stabilized with Polyelectrolyte

The high solid loading slurries with ZnO-Al2O3 powders stabilized with polyelectrolytes have been studied. The influence of Sodium poly(acrylate) (PA 30) on the fluidity and stablility of the slurries was investigated. Morphological features of ZnO-Al2O3 powders in suspension and fracture surface of green compact were observed using TEM and SEM. The slurries with pH 9 were prepared after milled using ZnO mixed powders and the PA 30 solution of pH 8. As 0.2 wt% PA 30 added, the lowest viscosity and the highest sediment were obtained. ZnO and Al2O3 particles had been homogeneous dispersed. The maximum density (66.7 %TD) of green compact was obtained.

Numerical Analysis of Impact Velocity on the Responses of Adhesively Bonded Steel Butt Joint with Material Properties

The effect of the impact velocity on the responses of the adhesively bonded steel butt joint during Izod impact test and the failure procedure is studied using the finite element method software ABAQUS. The results obtained show that the failure time of the element becomes little shorter when the impact velocity increased from 3.2 m/s to 10.2 m/s. The peak value of the Seqv in element 1 increases first and then decreased when the impact velocity reached 4.2 m/s. When the impact velocity is higher than 6.2 m/s, the peak value of the Seqv increased again as the impact velocity increased until 10.2 m/s. It is recommended that the impact velocity of 3.2 m/s or 5.2 m/s is suitable for Izod impact test for the adhesively bonded steel butt joint.